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A Sensitive Carbon Dioxide Sensor Based on Photoacoustic Spectroscopy with a Fixed Wavelength Quantum Cascade Laser
摘要： A photoacoustic spectroscopy (PAS) based carbon dioxide (CO2) sensor with a fixed wavelength quantum cascade laser (FW-QCL) was demonstrated. The emission wavelength of the FW-QCL at 4.42 μm in the mid-infrared spectral region matched a fundamental CO2 absorption line. Amplitude modulation of the laser intensity was used to match the resonant photoacoustic (PA) cell. The noise from the background was reduced with the correlation demodulation technique. The experimental results showed that the sensor had excellent signal stability and a concentration linear response. When the integration time was 1 s, a 1σ minimum detection limit (MDL) of 2.84 parts per million (ppm) for CO2 detection was achieved. The long-term stability of the sensor was evaluated by means of an Allan deviation analysis. With an integration time of ~100 s, the MDL was improved to 1 ppm. This sensor was also used to measure the CO2 concentration from some common emission sources, such as cigarette smoking, automobile exhaust, and the combustion of some carbon-containing materials, which confirmed the stability and robustness of the reported FW-QCL based CO2-PAS sensor system.
关键词： carbon dioxide detection,photoacoustic spectroscopy,quantum cascade laser
更新于2025-09-19 17:13:59
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Effects of 10,600?nm Carbon Dioxide Laser on Remineralizing Caries: A Literature Review
摘要： Objective: To study the effects of carbon dioxide (CO2) lasers (k = 10,600 nm) on remineralizing dental caries. Methods: This study involved performing a systematic search of English articles archived in the PubMed, Scopus, and Web of Science databases. The keywords used to identify the relevant articles were ((CO2 laser) OR (carbon dioxide laser)) AND ((dental caries) OR (tooth remineralization)). Publications before 2019 were selected. The titles and abstracts of the initially identi?ed articles were screened. Duplicate records, reviews, and irrelevant studies were removed. Full texts were retrieved for publications that studied the effects of CO2 lasers on remineralizing dental caries. Results: The search identi?ed 543 potentially relevant publications. A total of 285 duplicate records were removed. Sixteen articles were included in this review. Four studies reported that CO2 lasers inhibited bacterial growth. The growth of cariogenic bacteria, mainly Streptococcus mutans, on an irradiated tooth surface was slower compared with nonirradiated ones. Four studies investigated the reduction of the demineralization of enamel with cariogenic challenge. They found that CO2 lasers reduced the carbonate content of mineralized tissues and increased the microhardness of enamel. Nine studies used CO2 lasers associated with topical ?uorides in remineralizing dental caries. The results of the synergistic effect of laser irradiation and ?uoride application with regard to the inhibition of caries progression varied among these studies, whereas laser irradiation could enhance ?uoride uptake to demineralized mineral tissues. Conclusions: CO2 laser irradiation increased acid resistance and facilitated the ?uoride uptake of caries-like lesions. In addition, it reduced the growth of cariogenic bacteria.
关键词： carbon dioxide lasers,dental caries,?uoride,review,remineralization
更新于2025-09-19 17:13:59
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A portable miniaturized laser heterodyne radiometer (mini-LHR) for remote measurements of column CH4 and CO2
摘要： We present the design of a portable version of our miniaturized laser heterodyne radiometer (mini-LHR) that simultaneously measures methane (CH4) and carbon dioxide (CO2) in the atmospheric column. The mini-LHR fits on a backpack frame, operates autonomously, and requires no infrastructure because it is powered by batteries charged by a folding 30 W solar panel. Similar to our earlier instruments, the mini-LHR is a passive laser heterodyne radiometer that operates by collecting sunlight that has undergone absorption by CH4 and CO2. Within the mini-LHR, sunlight is mixed with light from a distributive feedback (DFB) laser centered at approximately 1.64 μm where both gases have absorption features. The laser scans across these absorption features roughly every minute and the resulting beat signal is collected in the radio frequency (RF). Scans are averaged into half hour and hour data products and analyzed using the Planetary Spectrum Generator (PSG) retrieval to extract column mole fractions. Instrument performance is demonstrated through two deployments at significantly different sites in interior Alaska and Hawaii. The resolving power (λ/?λ) is greater than 500,000 at 1.64 μm with precisions of better than 20 ppb and 1 ppm for CH4 and CO2, respectively. Because mini-LHR instruments are portable and can be co-located, they can be used to characterize bias between larger, stationary, column observing instruments. In addition, mini-LHRs can be deployed quickly to respond to transient events such as methane leaks or can be used for field studies targeting geographical regions.
关键词： atmospheric column,carbon dioxide,methane,portable,miniaturized laser heterodyne radiometer
更新于2025-09-19 17:13:59
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Applicability of a gas analyzer with dual quantum cascade lasers for simultaneous measurements of N2O, CH4 and CO2 fluxes from cropland using the eddy covariance technique
摘要： We evaluated the applicability of a closed-path gas analyzer with two mid-infrared quantum cascade lasers (QCLs) for simultaneous measurement of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a cropland using the eddy covariance (EC) technique. The measurements were carried out in a typical vegetable field in the subtropical China during the wintertime, when the gas fluxes are at their lowest level in the year. A new approach was proposed to optimize the determination of lag times between the wind and gas concentration data, which was proven efficient to increase the reliability of the measured fluxes when the gas exchanges are weak. The dual-QCL analyzer showed a median precision (1σ) of 0.14 nmol mol?1 for N2O, 3.3 nmol mol?1 for CH4 and 0.36 μmol mol–1 for CO2 at sampling frequency of 10 Hz under the field conditions. Such precisions are better than, or comparable with, those of other commonly used closed-path or open-path gas analyzers, which are capable of measuring only one or two of the three gases. The detection limit of the EC system for measuring half-hourly fluxes were 0.05 nmol m?2 s?1 for N2O, 1.12 nmol m?2 s?1 for CH4 and 0.14 μmol m–2 s–1 for CO2. The results showed that 100% of the N2O, 87% of the CH4 and 96% of the CO2 fluxes were larger than the above detection limits. This study suggests that the EC technique using a closed-path gas analyzer with two quantum cascade lasers is qualified for reliable and simultaneous measurements of N2O, CH4 and CO2 fluxes from a subtropical cropland throughout the year. Moreover, EC method based on this type of gas analyzer provides an additional option for long-term and simultaneous flux measurements of the three greenhouse gases in a wide range of agricultural and natural ecosystems.
关键词： Nitrous oxide,eddy covariance,cropland,methane,flux,quantum cascade laser,carbon dioxide
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Metrological assessment of the indirect method of measuring the concentration of oxygen in the air
摘要： Greenhouse Gases Observing Satellite (GOSAT), which measures column-averaged carbon dioxide dry air mole fractions (Xco2) from space, provides new data sources to improve our understanding of carbon cycle. The available GOSAT data, however, have many gaps and are irregularly positioned, which make it difficult to directly interpret their scientific significance without further data analysis. Spatio-temporal geostatistical prediction approach can be used to fill the gaps for global and regional Xco2 mapping. It is important to choose a suitable spatio-temporal variogram model since modeling spatio-temporal correlation structure using variogram model is a critical step in the geostatistical prediction. In this study, three different flexible spatio-temporal variogram models, including the product-sum model, Cressie–Huang model, and Gneiting model, are used to model the spatio-temporal correlation structure of Xco2 over China, using the Atmospheric CO2 Observations from Space retrievals of the GOSAT (ACOS-GOSAT) Xco2 (v3.3) data products. The three models are compared and evaluated using the weighted mean square errors (WMSE) indicating the fitness between the empirical variogram surface and the theoretical variogram model, cross-validation for quantifying prediction accuracies, and the performance of the three models when used to fill the spatial gaps and generate Xco2 maps in 3-day temporal interval. The results indicate that 1) the model fitness of the commonly used product-sum model is slightly better than Cressie–Huang model and Gneiting model as indicated from WMSE, and 2) all the three models present similar summary statistics in cross-validation, all with a significantly high correlation coefficient of 0.92, and about 83% of prediction error within 2 ppm and about 53% within 1 ppm, and (3) differences between the mapping results using the three models are generally less than 0.1 ppm, and no significant differences can be identified. As a conclusion from the above results, all the three variogram models can precisely catch the empirical characteristics of the spatio-temporal correlation structure of Xco2 over China, and the precision and effectiveness of predicting and mapping Xco2 using the three models are almost the same.
关键词： spatio-temporal kriging,spatio-temporal variogram models,carbon dioxide,mapping,ACOS-GOSAT
更新于2025-09-16 10:30:52
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Formation of Nanoparticles and Plasmonic Structures in Porous Materials Using Laser and SCF Technologies
摘要： A review of the authors’ studies on the processes of metal nanoparticles (silver and gold) formation and of various type structures in polymer and porous materials based on the effects of self-assembly and self-organization in the continuous laser radiation field is presented. Most experiments were performed either with samples saturated with metal precursors in supercritical carbon dioxide or with those exposed to this medium. Structures of various types from metal nanoparticles in polymers and porous glasses: periodic structures of micron and submicron scale, layered structures from nanoparticles with an unusually short period (about 90 nm), filament, ring structures, and island nanoparticle films have been synthesized. Several regularities and mechanisms of the formation of both the nanoparticles and their structures depending on the wavelength of laser radiation have been established. New results on the method for producing composite porous foam materials based on silver nanoparticles and polymer matrices, which combines laser-induced “drawing” of porous structures, their impregnation with precursor molecules using supercritical fluid technology, and subsequent reduction of nanoparticles are presented.
关键词： structures,porous glasses,polymers,carbon dioxide,supercritical fluid,nanoparticles,laser formation,self-assembly
更新于2025-09-16 10:30:52
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Phase-equilibrium measurement of a carbon dioxide/toluene/polystyrene ternary system using laser turbidimetry
摘要： The phase behavior of a carbon dioxide (CO2)/toluene (Tol)/polystyrene (PS) ternary system was measured. The measurements were performed using a synthetic method combined with a reflected light intensity measurement. The bubble points were determined by visual observation, and the cloud points were determined from the change in the reflected light intensity. The phase boundaries were measured at temperatures ranging from 313.2 K to 373.2 K and CO2 weight fractions ranging from 0.10 to 0.41. The homogeneous phase area decreased when the molecular weight of PS and/or the ratio of PS to Tol increased. It was found that the phase behavior of ternary systems, especially the liquid-liquid phase separation behavior, was altered by a change in the mutual solubility between the three components.
关键词： Toluene,Synthetic method,Carbon dioxide,Vapor-liquid equilibrium,Vapor-liquid-liquid equilibrium,Polystyrene,Laser turbidimetry,Liquid-liquid equilibrium
更新于2025-09-16 10:30:52
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Near-infrared tunable diode laser absorption spectroscopy-based determination of carbon dioxide in human exhaled breath
摘要： A spectroscopic detection system for the accurate monitoring of carbon dioxide (CO2) in exhaled breath was realized by tunable diode laser absorption spectroscopy (TDLAS) in conjunction with a vertical-cavity surface-emitting laser (VCSEL) and a multipass cell with an effective optical path-length of 20 m. The VCSEL diode emitting light with an output power of 0.8 mW, covered the strong absorption line of CO2 at 6330.82 cm?1 by drive-current tuning. The minimum detectable concentration of 0.769% for CO2 detection was obtained, and a measurement precision of approximately 100 ppm was achieved with an integration time of 168 s. Real-time online measurements were carried out for the detection of CO2 expirograms from healthy subjects, different concentrations were obtained in dead space and alveolar gas. The exhaled CO2 increased significantly with the increasing physical activity, reaches its maximal value at the beginning of respiratory compensation and then decreased slightly until maximal exercise. The developed measurement system has a great potential to be applied in practice for the detection of pulmonary diseases associated with CO2 retention.
关键词： CO2,human health monitoring,Tunable diode laser absorption spectroscopy,carbon dioxide,VCSEL,exhaled breath,TDLAS,vertical-cavity surface-emitting laser
更新于2025-09-16 10:30:52
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Laser absorption spectroscopy of rare and doubly-substituted carbon dioxide isotopologues
摘要： Unambiguous detection of the clumped carbon dioxide isotopologue 13C16O18O with isotope ratio mass spectrometry is difficult due to isobaric interference on m/z = 47. We present an analytical technique based on direct absorption laser spectroscopy for precise, direct and simultaneous detection of all isotopologues involved in the isotope exchange reaction 12C16O2 + 13C16O18O ? 12C16O18O +13C16O2 and of 12C16O17O. The achieved precision of 2×10-5 for the 13C16O18O/13C16O2 and 12C16O18O/12C16O2 isotopologue ratios allows to determine the equilibrium constant K of the isotope exchange reaction with an external reproducibility of better than 2×10-5 (1σ) after 9 reference-sample comparisons. Each comparison requires 7 minutes. The isotopic composition of the pure gas can be simultaneously analyzed with a precision of 0.05‰ (1σ) for δ13C and δ18O, and 0.15‰ (1σ) for δ17O. The instrument deploys two interband cascade lasers (ICL) with center wavelengths of 4.3 μm and 4.4 μm. A custom-built optical cell has been designed for single pass and multi pass optical paths (pathlength ratio 1:100); it allows simultaneous detection of rare and abundant isotopologues. The setup is capable to analyze pure CO2 samples of ～100 μmol.
关键词： clumped isotope analysis,mid-IR lasers,tunable lasers,doubly substituted isotopologues,carbon dioxide,laser spectroscopy,laser absorption
更新于2025-09-12 10:27:22
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Rapid and Precise Analysis of Carbon Dioxide Clumped Isotopic Composition by Tunable Infrared Laser Differential Spectroscopy
摘要： The high precision measurement of doubly-substituted (“clumped”) isotopologues in CO2 is a topic of significant interest in isotope geochemistry. Here we describe the performance of a new isotope ratio laser spectrometer using tunable infrared laser differential absorption spectroscopy (TILDAS). The TILDAS instrument has two continuous-wave lasers to simultaneously measure the four isotopologues involved in the 12C16O2 + 13C16O18O ? 13C16O2 + 12C16O18O exchange reaction. CO2 samples are trapped in a low volume (~250 ml) optical multi-pass cell with a path length of 36 meters. Each sample is compared to a reference gas, and clumped isotopologue precision of 0.01‰ (S.E.) is achieved within 20 minutes for 15 μmol samples. Similar precision is also achieved for bulk isotopic composition. The degree of rare isotope clumping in excess of strictly random distribution (?16O13C18O) measured by this TILDAS instrument varies linearly with theoretically calculated values and shows a very weak dependence on bulk isotopic composition.
关键词： TILDAS,laser spectroscopy,clumped isotopes,isotope geochemistry,carbon dioxide
更新于2025-09-12 10:27:22